1. Technical Field
The present invention relates to modulation techniques for optical transmission systems, and more particularly to multi-dimensional modulation techniques which take advantage of low density parity check coding.
2. Description of the Related Art
In recent years, optical communication systems have been evolving rapidly to adapt to the continuous increase in telecommunication needs. One major respect in which optical systems must improve is represented by the continuously increasing demand on transmission capacity. Such a demand stems mainly from the growing popularity of multimedia in everyday life. Unfortunately, adapting to higher transmission rates brings with it various obstacles, such as degradation in the signal quality as well as increased costs. Signal degradation is a result of linear and non-linear effects such as polarization mode dispersion and intrachannel nonlinearities. Non-linear effects become more pronounced at higher symbol rates.
Consequently, new optical communications solutions have to offer affordable upgrades to currently available optical communication systems that operate at lower speeds to satisfy the demand for higher speeds. This presents a dual benefit concept for approaching this problem: Utilizing currently available components avoids the added cost of producing faster, more complex components and avoids at the same time the augmented degradation of performance that accompanies higher speed components that results from the increase in non-linear effects.